How to use MERGE to create or reuse a part of pattern?

Question

I have node PRODUCT with multiple REVIEW node. I would create node PRODUCE if the product is not exist, then bind with REVIEW.

For the example, I want a PRODUCE node {n

Answer 1

Your subsequent match/merge is redundant. You can do:

// create/reuse PRODUCT
MERGE (product:PRODUCT {name:'X phone'})  
MERGE (product)-[:RATE]-(:REVIEW {content:'nope'})
MERGE (product)-[:RATE]-(:REVIEW {content:'best phone ever'})
MERGE (product)-[:RATE]-(:REVIEW {content:'worst phone ever'})